The present invention relates to a coated cemented carbide cutting tool insert particularly useful for turning operations in steels or stainless steels, and is especially suited for operations with high demands regarding toughness properties of the insert.
High performance cutting tools must nowadays possess high wear resistance, high toughness properties and good resistance to plastic deformation. Improved toughness behaviour of a cutting insert can be obtained by increasing the WC grain size and/or by raising the overall binder phase content, but such changes will simultaneously result in significant loss of the plastic deformation resistance.
Methods to improve the toughness behaviour by introducing an essentially gamma phase-free and binder phase-enriched surface zone with a thickness of about 20-40 μm on the inserts by so-called “gradient sintering” techniques have been known for some time e.g. U.S. Pat. Nos. 4,277,283, 4,497,874, 4,548,786, 4,640,931, 5,484,468, 5,549,980, 5,649,279, 5,729,823. The characteristics of these patents are that the surface zone has a different composition than the bulk composition, and is depleted of gamma phase and binder phase enriched.